Ammonium uptake in the nitrophytic lichen <b><i>Xanthoria parietina</i></b> and its effects on vitality and balance between symbionts

Abstract

The aim of this investigation was to determine the NH 4 Cl concentration threshold, above which negative physiological effects would occur in the nitrophytic lichen Xanthoria parietina . Over a 10 month period, X. parietina thalli growing on roof tiles were exposed weekly to NH 4 Cl concentrations of 0·04, 0·17, 0·34 or 0·69 M. Nitrogen (N) uptake from ammonium and the concentrations of total thallus N and biont markers (chlorophyll a , ergosterol and chitin) were measured on four occasions, over the experimental period. Xanthoria parietina was able to assimilate a significant quantity of the applied ammonium. However, lichens exposed to the two higher concentrations suffered damage to both the photobiont and the mycobiont, as evidenced by reduced chlorophyll a and ergosterol concentrations, while lichens exposed to the two lower concentrations showed no significant changes in either chlorophyll a or ergosterol that could be related to the ammonium inputs. Xanthoria parietina tolerated a weekly irrigation of at least 0·17 M NH 4 Cl, corresponding to an N deposition of c . 1000 kg ha −1 yr −1 , suggesting that this species has a very high tolerance to N pollution.